If you do go for a game focused on adventure/dungeon-based resources, how would that work? It sounds like we're making a sort of narrative-gamist system, which will irk folks who like simulationism.
Theoretical:
The DM gets an adventure challenge budget, and the PCs get a plot agency budget. The Challenge budget works kind of like the XP-based encounter budget of 4e.
The DMG would explain, "There are two primary ways to approach adventure design -- as a game, or as a simulation. In gamist design, the PCs will almost always deal with situations they are equipped for and capable of defeating, though they will be challenged in the process. In simulationist design, the world has challenges of many different sorts, some of which will be easy or too hard for the PCs.
"In a gamist adventure, you'll want to use the suggested Adventure XP budget for your party's level. This will ensure a fair challenge for the group.
"In a simulationist adventure, first determine what the challenge is, then tally the XP value of that challenge. This will reveal the adventure's level. During the course of the game, you should provide strong clues to the players about how hard an adventure will be. The PCs can still choose to go on a difficult adventure, but with these rules you won't be surprised when the PCs are overwhelmed."
Sound good?
In 4e, encounters have a sort of inherent rising action because PCs have fewer HP than monsters, so early in a combat it can look like the monsters are winning. But PCs get healing surges whereas monsters do not, so the tide will usually turn in the PCs' favor.
5e would probably have a mechanic similar to this for whole adventures. The DM gets the Adventure budget, while PCs get Plot Agency, which are like healing surges for plot.
Hm, say for a 1st level party of 5, the GM gets an Adventure Budget of 2000 XP. This represents the total resources aligned against the PCs during the course of the adventure - monsters, traps, and 'skill challenges' (or whatever supersedes them).
Likewise, the PCs get some sort of Plot Agency, say 300 per person, with Plot Surges that they can use to get more. These are a weird mix of physical health, social standing, luck, pluck, and cunning. They replace hit points and healing surges, and instead of representing how close to death you are, they represent how close to failure you are.
Every time a PC does something -- makes an attack, makes a check for a skill challenge, etc. -- he can just make the roll, or spend some of his Plot Agency to ensure a success. (And maybe when you design your PC, you could choose a few dramatic conventions, one of which you activate whenever you spend a Plot Surge -- allies show up, or you turn an enemy to your side, some environmental threat appears, you suddenly become a bad-ass, etc.)
The trick is balancing a GM's threats against the PC plot agency. The way a session would generally go, though, is that the PCs would be doing well, but they'd be slightly outmatched by the challenges. As they spend Plot Agency to stay alive, things get more and more dire, but then at just the right moment, the PCs start spending their Plot Surges, and they turn things around.
Of course, it's a tall order to take a system like that and make it feel real. You'd need to have attacks that can cause actual wounds with consequences; the PCs could spend Plot Agency to avoid those wounds, but still, they'd be aware of the threat. That way it would feel less like "the monster's claws bounce off you for 15 damage," and more like "the monster's claws graze you, but you avoid getting disemboweled by spending 15 PA."
That's probably too out there, though.
